<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
</head>
<body>
    <div id="app">
       <input type="text" v-model='num1'>
       <select name="" id="" v-model='operato'>
           <option value="+">+</option>
           <option value="-">-</option>
           <option value="*">*</option>
           <option value="/">/</option>
       </select>
       <input type="text" v-model='num2'>
       <button @click='calc'>=</button>
       <span>{{result}}</span>
    </div>
    <script>
        const vm =new Vue({
            el:'#app',
            data:{
                num1:'',
                num2:'',
                operato:'+',
                result:''
             
            },
            methods:{
                calc(){
                    this.num1=Number(this.num1)
                    this.num2=Number(this.num2)
                    switch(this.operato){
                        case '+':
                        this.result=this.num1+  this.num2
                        break
                        case '-':
                        this.result=this.num1-  this.num2
                        break
                        case '*':
                        this.result=this.num1* this.num2
                        break
                        case '/':
                        this.result=this.num1/  this.num2
                        break
                    }
                }
            }
        })
    </script>
</body>
</html>